Modern internal combustion engines having fully variable valve drive may operate with electromagnetic valve control (EMVC), electrohydraulic valve control (EHVC) or with mechanical options such as a variable camshaft control (VACSC) for phase control in conjunction with a variable valve drive (VVD) for lift control. In electromechanical and electrohydraulic valve control, the engine does not include a camshaft, although a camshaft is may be present in the mechanical variants.
Because there is no camshaft, electromagnetic and electrohydraulic valve controls offer more degrees of freedom in controlling the opening, the closing and the lift of the intake and exhaust valves of an engine, e.g., a spark-ignition engine or a diesel engine. Using electromagnetic valve control, the opening angle and the closing angle of a valve may be controlled, and with electrohydraulic valve control, the opening angle and the closing angle, the opening speed and closing speed, as well as the lift of the corresponding valve may be controlled.
The possibility of individually controlling the intake valves and exhaust valves of each cylinder of the engine may allow improved engine operation.
U.S. Pat. No. 5,377,631 describes an internal combustion engine which is operated in a 6-, 8- or 12-stroke operation instead of the conventional 4-stroke operation. In this case, one or more cylinders are deactivated during engine operation in indirect proportion to the engine load. Fuel injection is suppressed in the deactivated cylinders and the intake and exhaust valves are closed with the downward and upward movement of the piston in the cylinder. Thus, the downward movement of the piston just creates a vacuum when the cylinder is deactivated, and the upward movement of the piston returns the internal pressure in the cylinder back to atmospheric pressure. This may allow unthrottled operation of the engine with less friction in deactivated cylinders, thus making available an engine having lower fuel consumption.
To reduce hydrocarbon emissions (HC emissions) immediately after starting a spark-ignition engine, it is conventional today to inject fresh air directly downstream from the exhaust valves of the engine by using an electric pump. Such a pump is referred to as a secondary air pump and may include secondary air valves, secondary air tubing and electric triggering. Fresh air induces oxidation of the hydrocarbons (HC) in the exhaust gas while the latter is still hot. This is referred to as secondary oxidation.
In the secondary oxidation described above, the spark-ignition engine may also be operated at a λ<1. This secondary oxidation of a fuel-air mixture creates an exothermic reaction, thus the catalytic converter may be arranged in an exhaust system of the spark-ignition engine to be rapidly heated up.
U.S. Pat. No. 4,075,837 describes an internal combustion engine in which a second intake duct, which is separate from a main intake duct and is connected to a single cylinder, is provided so that secondary air may be supplied downstream from the exhaust valves. An exhaust duct of this single cylinder includes connections to a main exhaust duct of the remaining cylinders, opening into the exhaust ducts directly downstream from the exhaust valves of the remaining cylinders. Therefore, secondary air is supplied in operating states in which the exhaust is purified further by supplying secondary air, i.e., by suppressing a fuel supply and an ignition operation in this one cylinder including the separate intake duct. Thus, the piston acts like a pump in this cylinder in which the fuel supply and ignition have been suppressed, drawing air in through the intake valve with a downward movement of the piston and, with the upward movement of the piston, when the intake valve is closed, pumping, through the exhaust duct of this cylinder, the fresh air in the cylinder as secondary air to the remaining cylinders.
According to U.S. Pat. No. 4,075,837, however, it is necessary to provide another intake duct, which is separate from the main intake duct, as well as another exhaust duct for the cylinder which is used as an air pump. This increases the cost and the required maintenance of the engine.